/**
 * Created with IntelliJ IDEA.
 * User: seth.yang
 * Date: 15-1-9
 * Time: 上午3:47
 * To change this template use File | Settings | File Templates.
 */
/*document.getElementById('close').onmousedown = function(e) {
    e.preventDefault();
    document.getElementById('info').style.display = 'none';
    return false;
};*/

// settings

var physics_accuracy = 5,
    mouse_influence      = 20,
    mouse_cut            = 5,
    gravity              = 1200,
    cloth_height         = 50,
    cloth_width          = 100,
    start_y              = 20,
    spacing              = 7,
    tear_distance        = 60;


window.requestAnimFrame =
    window.requestAnimationFrame       ||
        window.webkitRequestAnimationFrame ||
        window.mozRequestAnimationFrame    ||
        window.oRequestAnimationFrame      ||
        window.msRequestAnimationFrame     ||
        function(callback) {
            window.setTimeout(callback, 1000 / 60);
        };

var canvas,
    ctx,
    cloth,
    boundsx,
    boundsy,
    mouse = {
        down: false,
        button: 1,
        x: 0,
        y: 0,
        px: 0,
        py: 0
    };

window.onload = function() {

    canvas = document.getElementById('c');
    ctx    = canvas.getContext('2d');

    canvas.width = canvas.clientWidth;
    canvas.height = 500;

    canvas.onmousedown = function(e) {
        mouse.button = e.which;
        mouse.px = mouse.x;
        mouse.py = mouse.y;
        var rect = canvas.getBoundingClientRect();
        mouse.x = e.clientX - rect.left;
        mouse.y = e.clientY - rect.top;
        mouse.down = true;
        e.preventDefault();
    };

    canvas.onmouseup = function(e) {
        mouse.down = false;
        e.preventDefault();
    };

    canvas.onmousemove = function(e) {
        mouse.px = mouse.x;
        mouse.py = mouse.y;
        var rect = canvas.getBoundingClientRect();
        mouse.x = e.clientX - rect.left;
        mouse.y = e.clientY - rect.top;
        e.preventDefault();
    };

    canvas.oncontextmenu = function(e) {
        e.preventDefault();
    };

    boundsx = canvas.width - 1;
    boundsy = canvas.height - 1;

    ctx.strokeStyle = 'rgba(255, 128, 255,0.6)';
    cloth = new Cloth();
    update();
};

var Point = function(x, y) {

    this.x = x;
    this.y = y;
    this.px = x;
    this.py = y;
    this.vx = 0;
    this.vy = 0;
    this.pin_x = null;
    this.pin_y = null;
    this.constraints = [];
};

Point.prototype.update = function(delta) {

    if (mouse.down) {

        var diff_x = this.x - mouse.x,
            diff_y = this.y - mouse.y,
            dist   = Math.sqrt(diff_x * diff_x + diff_y * diff_y);

        if (mouse.button == 1) {

            if(dist < mouse_influence) {
                this.px = this.x - (mouse.x - mouse.px) * 1.8;
                this.py = this.y - (mouse.y - mouse.py) * 1.8;
            }

        } else if (dist < mouse_cut) this.constraints = [];
    }

    this.add_force(0, gravity);

    delta *= delta;
    nx = this.x + ((this.x - this.px) * .99) + ((this.vx / 2) * delta);
    ny = this.y + ((this.y - this.py) * .99) + ((this.vy / 2) * delta);

    this.px = this.x;
    this.py = this.y;

    this.x = nx;
    this.y = ny;

    this.vy = this.vx = 0
};

Point.prototype.draw = function() {

    if (this.constraints.length <= 0) return;

    var i = this.constraints.length;
    while(i--) this.constraints[i].draw();
};

Point.prototype.resolve_constraints = function() {

    if (this.pin_x != null && this.pin_y != null) {

        this.x = this.pin_x;
        this.y = this.pin_y;
        return;
    }

    var i = this.constraints.length;
    while(i--) this.constraints[i].resolve();

    this.x > boundsx ? this.x = 2 * boundsx - this.x : 1 > this.x && (this.x = 2 - this.x);
    this.y < 1 ? this.y = 2 - this.y : this.y > boundsy && (this.y = 2 * boundsy - this.y);
};

Point.prototype.attach = function(point) {

    this.constraints.push(
        new Constraint(this, point)
    );
};

Point.prototype.remove_constraint = function(lnk) {

    var i = this.constraints.length;
    while(i--) if(this.constraints[i] == lnk) this.constraints.splice(i, 1);
};

Point.prototype.add_force = function(x, y )  {

    this.vx += x;
    this.vy += y;
};

Point.prototype.pin = function(pinx, piny) {
    this.pin_x = pinx;
    this.pin_y = piny;
};

var Constraint = function(p1, p2) {

    this.p1 = p1;
    this.p2 = p2;
    this.length = spacing;
};

Constraint.prototype.resolve = function() {

    var diff_x = this.p1.x - this.p2.x,
        diff_y = this.p1.y - this.p2.y,
        dist = Math.sqrt(diff_x * diff_x + diff_y * diff_y),
        diff = (this.length - dist) / dist;

    if (dist > tear_distance) this.p1.remove_constraint(this);

    var px = diff_x * diff * 0.5;
    var py = diff_y * diff * 0.5;

    this.p1.x += px;
    this.p1.y += py;
    this.p2.x -= px;
    this.p2.y -= py;
};

Constraint.prototype.draw = function() {

    ctx.moveTo(this.p1.x, this.p1.y);
    ctx.lineTo(this.p2.x, this.p2.y);
};

var Cloth = function() {

    this.points = [];

    var start_x = canvas.width / 2 - cloth_width * spacing / 2;

    for(var y = 0; y <= cloth_height; y++) {

        for(var x = 0; x <= cloth_width; x++) {

            var p = new Point(start_x + x * spacing, start_y + y * spacing);

            x != 0 && p.attach(this.points[this.points.length - 1]);
            y == 0 && p.pin(p.x, p.y);
            y != 0 && p.attach(this.points[x + (y - 1) * (cloth_width + 1)]);

            this.points.push(p);
        }
    }
};

Cloth.prototype.update = function() {

    var i = physics_accuracy;

    while(i--) {
        var p = this.points.length;
        while(p--) this.points[p].resolve_constraints();
    }

    i = this.points.length;
    while(i--) this.points[i].update(.016);
};

Cloth.prototype.draw = function() {

    ctx.beginPath();

    var i = cloth.points.length;
    while(i--) cloth.points[i].draw();

    ctx.stroke();
};

function update() {

    ctx.clearRect(0, 0, canvas.width, canvas.height);

    cloth.update();
    cloth.draw();

    requestAnimFrame(update);
}